/* * 代碼清單8: subchannel.c */#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <fcntl.h>#include <sys/ioctl.h>#include <linux/cdrom.h>/* CD驅動器對應的設備文件 */#define DEVICE "/dev/cdrom"/* 返回CD當前狀態的字符串 */char* audiostatus(int status) {  switch(status) {  case CDROM_AUDIO_INVALID:  return "Invalid";  case CDROM_AUDIO_PLAY:      return "Playing";  case CDROM_AUDIO_PAUSED:    return "Paused";  case CDROM_AUDIO_COMPLETED: return "Completed";  case CDROM_AUDIO_ERROR:     return "Error";  case CDROM_AUDIO_NO_STATUS: return "Stopped";  defautl:                    return "Unknown";  }} int main() {  int fd;  int status;  struct cdrom_subchnl channel;  /* 打開設備 */  fd = open(DEVICE, O_RDONLY);  if (fd < 0) {    perror("unable to open " DEVICE);    exit(1);  }  while(1) {    /* 讀取子通道數據 */    channel.cdsc_format = CDROM_MSF; /* 采用MSF格式地址 */    status = ioctl(fd, CDROMSUBCHNL, &channel);    if (status != 0) {      perror("CDROMSUBCHNL ioctl failed");      exit(1);    }    /* 輸出CD的當前狀態 */    printf("Status: %s \n", audiostatus(channel.cdsc_audiostatus));    printf("Track: %d \n", channel.cdsc_trk);    printf("Postion: %02d:%02d:%02d(%02d:%02d:%02d) \n\n",           channel.cdsc_reladdr.msf.minute,           channel.cdsc_reladdr.msf.second,           channel.cdsc_reladdr.msf.frame,           channel.cdsc_absaddr.msf.minute,           channel.cdsc_absaddr.msf.second,           channel.cdsc_absaddr.msf.frame);    fflush(stdout);    usleep(100000);  }  /* 關閉設備 */  status = close(fd);  if (status != 0) {    perror("unable to close " DEVICE);    exit(1);  }  return 0;}